The present invention relates to sunscreening agents having improved adhesion to the skin, and to the preparation of said sunscreening agents.
"Sunscreens", synthetic compounds that absorb strongly in the ultraviolet region of the spectrum, have found wide use as protective agents against sunburn or erythema. Of the many compounds which have been tried over the years (E. G. Klarmann, Am. Perf. and Essential Oil Rev. 58 33-8 126-35 (1949) ) derivatives of salicylic acid, p-aminobenzoic acid, 2-hydroxybenzophenone and 2-hydroxyphenylbenzotriazole have emerged as the most desirable "sunscreens" from the practical as well as the theoretical point of view. However, as yet, no product is available which through regular use would impart convenient and constant protection against the damaging effects of ultraviolet radiation.
At least as early as 1946 it was recognized that one of the deficiencies of then existing "sun-tan" lotions was failure to protect because the sunscreen agent was diluted or floated off by perspiration. Resistance to water or sweat can be imparted to a degree by incorporating water repellents or emollients in the formulations. However, for various purposes such as more than occasional use and for incorporation in a variety of products it is advantageous to have, as an active agent or agents in a formulation, materials which not only absorb erythemal radiation but also adhere strongly to the skin.
Many compounds capable of absorbing ultraviolet radiation have been described in the literature and recommended as sunscreening agents. Among those recommended are the following:
______________________________________ TYPE SPECIFIC FORM ______________________________________ Aminobenzoic acids o- and p-aminobenzoates and anthranilates Hydroxybenzoic acids salicylates and tannates Cinnamic acid menthyl and benzyl esters Coumarins unbelliferones; quercetin; esculin; daphnin Biphenyls o- and p-dihydroxybiphenyl disulfonates Naphthols sulfonates and carboxylates Benzothiazoles condensations of aromatic aldehydes and aminothiophenol Imidazoles uric acid and histidine derivative; urocanic acid "Sulfa" drugs n',n'-Dimethyl-n.sup.4 -sulfanilyl- sulfanilamide; n.sup.4 -sulfanilyl- sulfanilamide Aromatic ketones benzalacetone; butyl-cinnamyl pyruvate Piperonals Benzophenones Highly purified, light yellow, powdered benzophenones, e.g., 2,2'-dihydroxy-4,4'-dimethoxy- benzophenone Hydrocarbons stilbenes acetanilide Vitamin C ______________________________________
Most of the foregoing and other materials having the capability of absorbing ultraviolet light have not proved satisfactory for use as sunscreen agents for one or more of the following reasons: coat, safety, discoloration of fabrics, among others. Some are not sufficiently selective between erythemal and tanning radiation. In spite of the deficiencies of the presently recognized sunscreening agents the most widely used at the present time are derivatives of aminobenzoic acid, salicylic acid, and the substituted benzophenones marketed under the tradename, "Uvinul."